Contrasted triangles on interface and transparent materials in viewport and material view
TL;DR: Your GPU does not fulfill the minimum requirements for running Blender 2.8x or later.

&quot;Turks&quot; is part of the codename of multiple GPUs that have the TeraScale 2 micro-architecture:

Radeon HD 6570 (Turks Pro)
Radeon HD 6570 (Turks Pro)
Radeon HD 6670 (Turks XT)
Radeon HD 7510 (Turks LE)
Radeon HD 7570 (Turks Pro-L)
Radeon HD 7670 (Turks XT)
FirePro V3900 (Turks GL)
FirePro V4900 (Turks XT GL)
FirePro M2000 (Turks GL)

In order to run Blender properly, your hardware has to fulfill the minimum requirements. For AMD graphics cards the micro-architecture has to be at least GCN first generation or later. This is to ensure normal operation, GPU rendering has higher requirements. At the time of writing the minimum requirements for graphics card for Blender 2.8x and 2.9x are:

Supported Graphics Cards

NVIDIA: GeForce 400 and newer, Quadro Tesla GPU architecture and newer, including RTX-based cards, with NVIDIA drivers (list of all GeForce and Quadro GPUs)
AMD: GCN 1st gen and newer (list of all AMD GPUs)
Intel: Haswell and newer (list of all Intel GPUs)
macOS: version 10.13 or newer with supported hardware


Unfortunately, this means that your GPU is below the minimum requirements and not officially supported. You may still be able to run Blender, but graphics glitches or even crashes, due to issues with the graphics driver, may occur. Sometimes the graphic glitches can be resolved by installing a more recent graphics driver, if one is available.
Blender 2.79b is the last release that officially supported your GPU. Previous versions of Blender can be download from this page.